Nitrogen Content Of Weld Metal Research Articles

The influence of shielding gases on keyhole-induced porosity and nitrogen absorption in SS 304 stainless steel fiber laser welds

Regarding porosity formation and gas content, choosing the appropriate shielding gas for laser welding is essential for achieving high-quality joints. Keyhole-induced porosity formation tendency and nitrogen content in SS 304 stainless steel welds were investigated based on the nitrogen content in shielding gases during fiber laser welding. Beads-on-plate autogenous welds were made at 5 kW continuous wave (CW) fiber laser in N2 and Ar mixtures. Optical metallography, micro-focused X-ray, X-ray radiography, and high-speed images of the molten pool were used to investigate the porosity formation. In addition, a gas analyzer was used to study the weld metal nitrogen content. The results show that nitrogen significantly impacts the reduction of porosity in the melting zone and increases the dissolved nitrogen in the solidified weld metal, as using pure nitrogen leads to an increase in dissolved nitrogen by 36% higher than the nitrogen content in the base metal. In contrast, it has almost no significant effect on the keyhole mode.

Promoting austenite formation in laser welding of duplex stainless steel\u2014impact of shielding gas and laser reheating

Avoiding low austenite fractions and nitride formation are major challenges in laser welding of duplex stainless steels (DSS). The present research aims at investigating efficient means of promoting austenite formation during autogenous laser welding of DSS without sacrificing productivity. In this study, effects of shielding gas and laser reheating were investigated in welding of 1.5-mm-thick FDX 27 (UNS S82031) DSS. Four conditions were investigated: Ar-shielded welding, N2-shielded welding, Ar-shielded welding followed by Ar-shielded laser reheating, and N2-shielded welding followed by N2-shielded laser reheating. Optical microscopy, thermodynamic calculations, and Gleeble heat treatment were performed to study the evolution of microstructure and chemical composition. The austenite fraction was 22% for Ar-shielded and 39% for N2-shielded as-welded conditions. Interestingly, laser reheating did not significantly affect the austenite fraction for Ar shielding, while the austenite fraction increased to 57% for N2-shielding. The amount of nitrides was lower in N2-shielded samples compared to in Ar-shielded samples. The same trends were also observed in the heat-affected zone. The nitrogen content of weld metals, evaluated from calculated equilibrium phase diagrams and austenite fractions after Gleeble equilibrating heat treatments at 1100 °C, was 0.16% for N2-shielded and 0.11% for Ar-shielded welds, confirming the importance of nitrogen for promoting the austenite formation during welding and especially reheating. Finally, it is recommended that combining welding with pure nitrogen as shielding gas and a laser reheating pass can significantly improve austenite formation and reduce nitride formation in DSS laser welds.

Microstructure and mechanical properties of welding metal with high Cr-Ni austenite wire through Ar-He-N2 gas metal arc welding

A high Cr-Ni austenite wire with 0.1% nitrogen was developed for gas metal arc welding of high strength low alloy (HSLA) steel (10Ni5CrMoV) to prevent hydrogen induced crack. The austenite weld joint without visible defects can be obtained using Ar + He + N2 shielding gas. When N2 content of shielding gas increased from 0% to 8%, the nitrogen content of weld metal rose from 0.10% to 0.19%, and other alloy content kept unchanged. The increasing of nitrogen content in weld metal made weld grains refined. It can improve mechanical properties of weld metal in different degrees including yield strength, tensile strength, elongation and impact toughness. However, with 8% N2 content of shielding gas, the massive microspores appeared in weld metal will decrease the welded joint properties. Therefore, 50%Ar + 45%He + 5%N2 was selected for welding of 10Ni5CrMoV HSLA steel using high Cr-Ni austenite wire.

Use of electron microprobe analysis to explain metallurgical phenomena and their effect on properties when welding stainless steel

A modified electron probe microanalysis (EPMA) instrument containing six wavelength dispersive spectrometers has been used for mapping cross-sections of stainless steel base material and welds. It made it possible to measure the composition in specific small areas and to illustrate element partitioning; ranging from centerline segregation to concealed sub-microstructure. Examples from industrial research are given to demonstrate the versatile application field for this established technology. EPMA was used to study the chemical composition of gas tungsten arc welds in the lean duplex grade UNS S32101 performed with and without nitrogen additions to the argon-based shielding gas. The level of nitrogen in the shielding gas not only determined the weld metal nitrogen content, but also affected evaporation of other elements from the weld metal. Mapping could also be used to reveal detailed information about the dendritic substructure in welds and the fusion line that could not be seen with conventional microscopy as the weld metal microstructure is controlled by nitrogen. With the measured local composition, it was possible to calculate the pitting resistance equivalent number, PRE = Cr + 3.3 × Mo + 16 × N (wt%) and thereby visualize the local variation in the microstructure. Nitrogen is strongly concentrated in the austenite and has the largest impact on the PRE. Pitting corrosion testing confirmed that the ferrite phase was most susceptible to pitting attack and that a higher average PRE does not significantly increase the critical pitting temperature. The EPMA instrument was also applied to study all-weld metal of E347T0 type flux-cored wire with and without bismuth additions. Bismuth can have a negative effect on weld metal ductility after post-weld heat treatment and/or applications at high temperature. It has been suggested that this is due to grain boundary bismuth segregation, and it has been debated whether it occurs as bismuth or bismuth oxide Bi2O3. Hot tensile testing confirmed that the bismuth content affects the weld metal ductility at 700 °C and EPMA proved that bismuth segregates as round particles after post-weld heat treatment and not as bismuth oxide.

The elimination of pores in laser welds of AISI 304 plate using different shielding gases

A laser power of 10kW was used to weld 304 stainless steel. Different shielding gases including Ar, N2 and no gas were used. The porosity in the laser welds was examined. The metallic plume, liquid melt pool and laser keyhole were observed by a high-speed video camera. Bubbles were produced in all the laser welds. Many pores were retained in the 304L stainless steel laser welds made in Ar. Almost no pores were found in the laser welds made in N2 or no shielding gas. The dissolution of N2 bubbles in the liquid melt pool led to the elimination of the pores in the 304L laser welds. The retention time of liquid melt pool was 1.1s at a laser power of 10kW and a welding speed of 0.8m/min. It took 30μs to absorb all the N2 bubbles in the liquid melt pool. The increase of the nitrogen content in weld metal was 3.4×10−5wt.%.

Effects of nitrogen and hydrogen in argon shielding gas on bead profile, delta-ferrite and nitrogen contents of the pulsed GTAW welds of AISI 316L stainless steel

AbstractThe general effects of 1, 2, 3 and 4 vol.-% nitrogen and 1, 5 and 10 vol.-% hydrogen in argon shielding gas on weld bead profile (depth/width ratio: D/W) and the δ-ferrite content of AISI 316L pulsed GTAW welds were investigated. The limits for imperfections for the quality levels of welds were based on ISO 5817 B. The plates with a thickness of 6 mm were welded at the flat position and the bead on plate. Increasing hydrogen content in argon shielding gas increases the D/W ratio. Excessive hydrogen addition to argon shielding gas will result in incompletely filled groove and excessive penetration of weld. Increasing welding speed decreases the weld-metal volume and the D/W ratios. Nitrogen addition to argon shielding gas has no effect on the D/W ratio. The addition of a mixture of nitrogen and hydrogen to argon shielding gas on the D/W ratio does not show any interaction between them. An effect on the D/W ratio can be exclusively observed as a function of hydrogen content. Increasing hydrogen content in argon shielding gas increases the δ-ferrite content of weld metal. Increasing either nitrogen content in shielding gas or welding speed decreases the δ-ferrite content of weld metal. The nitrogen addition increases the weld metal nitrogen content, however, the hydrogen addition leads to a decrease of weld metal nitrogen content.

Nitrogen absorption phenomenon of GTA welding with nitrogen-mixed shielding gases: effect of plasma characteristics on nitrogen content in GTA welded metal

In order to clarify the nitrogen absorption mechanism in gas tungsten arc welding, the measurement of the weld metal nitrogen content under nitrogen mixture shielding gases, and the numerical analysis of plasma heat source characteristics in nitrogen dissociation phenomenon were conducted. The nitrogen content of weld metal produced by He arc reduces to approximately a half relative to that by Ar arc in the shielding gas condition of less than about 1% mixture ratio. Additionally, it is assumed that a decline in the plasma temperature in the vicinity of the molten pools due to the generation of metal vapour, accompanied by a reduction in atom-like nitrogen content, cause intense impact on the reduction mechanism of weld metal nitrogen content in a He arc.

Effects of TIG Pulse Current and Nitrogen Content in Argon Shielding Gas on Microstructure and Mechanical Properties of 15Cr-4Ni-8Mn-1.3Cu Stainless Steel Weld Metal

The TIG pulse welding of 15Cr-4Ni-8Mn-1.3Cu austenitic stainless steel at pulse currents of 130 and 160 A with Argon shielding gases containing 0%, 5% and 10% (v/v) Nitrogen was investigated. The effects of pulse current and Nitrogen content in Argon shielding gas on the microstructure and mechanical properties of weld metal were studied. Based on the results found in this study, the nitrogen content in weld metal was found to increase with increasing nitrogen content in argon shielding gas and pulse current. With the addition of nitrogen in Argon shielding gas, the morphology of delta-ferrites was changed from the conventional TIG pulse welding using pure Argon shielding gas where both lathy and vermicular types were found. However, with the Nitrogen + Argon shielding gas, only vermicular type was observed. Moreover, the arm spacing of delta-ferrite can be enlarged by increasing the pulse current. Those results are the reason for the observed decrease in tensile strength and percent elongation with increasing nitrogen content in argon shielding gas and the pulse current.

Effect of plasma heat source characteristics on nitrogen absorption in gas tungsten arc weld metal

Effects of plasma heat source characteristics on nitrogen absorption in gas tungsten arc (GTA) weld metal was investigated using two-dimensional spectroscopic measurements and numerical analyses. In the condition of 1 % nitrogen-mixed shielding gas, nitrogen content of weld metal in a helium arc or an argon-hydrogen arc decreased compared to that of an argon arc. These changes in nitrogen content had a strong correlation with arc voltages for the respective shielding gases, so it was considered that nitrogen absorption in weld metal was affected by arc plasma heat source characteristics. The spectroscopic measurements of these arcs showed that the plasma temperature near the molten pool surface in the helium arc or the argon-hydrogen arc indicated around 6,500 K, while the plasma temperature in the argon arc achieved more than 10,000 K. Additionally, from numerical analyses of GTA dealing with metal vapor, it was found that the plasma temperature in the helium arc was reduced by the metal vapor generated from the molten pool. As a result, the reduction of nitrogen disassociation caused by decreasing plasma temperature was considered as the significant factor in lowering nitrogen absorption in the helium arc.

窒素混合シールドガスを用いたGTA溶接における溶接金属の窒素吸収現象

In order to clarify the nitrogen absorption mechanism in gas tungsten arc welding, the measurement of the weld metal nitrogen content under nitrogen mixture shielding gases, and the numerical analysis of plasma heat source characteristics in nitrogen dissociation phenomenon were conducted. The nitrogen content of weld metal produced by He arc reduces to approximately a half relative to that by Ar arc in the shielding gas condition of less than about 1% mixture ratio. Additionally, it is assumed that a decline in the plasma temperature in the vicinity of the molten pools due to the generation of metal vapor, accompanied by a reduction in atom-like nitrogen content, cause intense impact on the reduction mechanism of weld metal nitrogen content in a He arc.

The Behaviour of Nitrogen on the Welding Parameters of the Dissimilar Weld Joints between AISI 304 and AISI 316L Austenitic Stainless Steels Produced by Gas Tungsten Arc Welding

The behavior of nitrogen into the dissimilar joining metal between AISI 304 and AISI 316L Austenitic stainless steel during gas tungsten are welding process was investigated. Studied by using an arc nitrogen atmosphere – controlling in chamber. The relations between nitrogen content of the dissimilar weld metal and the welding parameters, such as the welding current, welding speed, welding arc length and penetration area of weld metals were also evaluated. The results show that the nitrogen content of the weld metals decreased with an increasing welding current, and increasing penetration areas of weld metal, but scarcely depends on the welding arc length. The nitrogen content of the weld metals increased with the welding speed, but decreased penetration areas of weld metals. The role of nitrogen content on the dissimilar weld metals stainless steel is further confirmed by the experimental microstructure, mechanical and corrosion behaviour of the weld metal.

Shielding Gas Oxygen Additions as a Means of Curbing Nitrogen Degassing During the Autogenous Arc Welding of Nitrogen-Alloyed Stainless Steel

This study examined the influence of oxygen additions (0.5% to 2.0%) to argon-rich shielding gas on nitrogen degassing during the autogenous arc welding of a high-manganese nitrogen-alloyed austenitic stainless steel, previously commercially available under the trade name of Cromanite. Autogenous arc welding of this steel in inert shielding gas results in considerable nitrogen losses from the weld pool, characterised by an unstable arc, spattering and violent metal expulsion from the weld pool. Oxygen additions to the shielding gas stabilise the arc and curb nitrogen-induced porosity, but at least 2.0% oxygen (by volume) is required to maintain the weld metal nitrogen content at the level of the parent material prior to welding. The beneficial effect of oxygen additions to the shielding gas is attributed to the formation of a solid MnCr2O4 spinel phase on the weld pool surface during welding, which retards nitrogen degassing by reducing the area available for the adsorption of nitrogen atoms prior to their recombination to form N2. This layer has a granular, irregular appearance and presents a less effective barrier to nitrogen degassing than the continuous, uniform liquid slag layer that forms when the Cr-Ni 300-series austenitic stainless steels are welded in oxygen-containing shielding gas mixtures.

The Influence of Interstitial Diffusion Across the Fusion Line on the HAZ Microstructure and Properties in 12% Chromium Type 1.4003 Steels

The 12% chromium type EN 1.4003 ferritic stainless steels are susceptible to grain growth and associated embrittlement in the heat-affected zone during welding. Grain growth can be restricted by increasing the amount of austenite that forms on cooling through the dual-phase (austenite+ferrite) field. This investigation examined ways of locally increasing the interstitial (carbon or nitrogen) content of the heat-affected zone during welding, and studying the effect of such an increase in interstitial content on the microstructure and mechanical properties of the welded joints. Significant changes in heat-affected zone microstructure and mechanical properties were observed on increasing the carbon content of the weld metal through the use of a higher-carbon welding consumable, and on increasing the weld metal nitrogen content through the use of nitrogen-containing shielding gas. This suggests that the weld thermal cycle is sufficiently long to allow diffusion from the weld metal across the fusion line into the high temperature heat-affected zone, resulting in higher levels of martensite, smaller ferrite grain sizes, higher heat-affected zone hardness values, and improved toughness.

Porosity and Nitrogen Content of Weld Metal in Laser Welding of High Nitrogen Austenitic Stainless Steel

Some problems such as nitrogen desorption and pores always occur in the weld metal during welding of high nitrogen steel. In order to study the nitrogen content and porosity of the weld metal of high nitrogen steel 1Cr22Mn16N, the steel was welded by CO2 laser welding, and the influence of the shielding gas composition and heat input on the nitrogen content and porosity of the weld metal was investigated. The experimental results indicate that the weld nitrogen content increases slightly with the increase of the nitrogen content in shielding gas under the same laser welding conditions. The nitrogen content of the weld metal decreases with the increase of the heat input when pure argon is used as the shielding gas, whereas that of the weld metal is improved with the increase of the heat input when some nitrogen is added to the shielding gas. The higher the heat input, the less the porosity in the weld metal, and the more nitrogen in the shielding gas, the less the porosity becomes.

The relationship between impact strength and the manganese, nickel, molybdenum and nitrogen content of weld metal deposited with low-hydrogen, low-alloy electrodes

The relationship between impact strength and the manganese, nickel, molybdenum and nitrogen content of weld metal deposited with low-hydrogen, low-alloy electrodes

High Nitrogen Steels. Nitrogen Content of 316L Weld Metal and Its Fine Particle by Means of High-pressure MIG Arc Welding.

The suitability of the high nitrogen pressure Metal Inert Gas (MIG) ARC welding process (constant arc length condition) for high nitrogen containing stainless steel was investigated. The formation of the stainless steel fine particles by the high nitrogen pressure MIG arc welding process was examined. The welding atmosphere consisted of pressurized N2 gas. Nitrogen absorption of 316L stainless steel weld metal and its fine particle in the high nitrogen pressure MIG process was studied. The effect of nitrogen contents in remelted weld metal and changes in teh microstructure of the weld metal were observed. The nitrogen content of weld metal and the number of fine particles increased with increasing pressure of N2. Approximately 0.6 and 2.4 mass% nitrogen was absorbed in the weld metal and fine particles at pressure of N2 6 MPa and 3 MPa nitrogen, respectively. Nitrogen content of the weld metal was lower than that representing equilibrium solubility of 316L stainless steel at colse to the melting point.

High Nitrogen Steels. Influence of Shielding Gas Composition and Welding Parameters on the N-content and Corrosion Properties of Welds in N-alloyed Stainless Steel Grades.

TIG welding using different heat inputs, arc lengths and shielding gas nitrogen contents was performed. The aim was to evaluate the possibilities to avoid nitrogen losses on welding or even increase the weld metal nitrogen content and thereby improve the corrosion properties and, in the case of duplex grades, also to improve the phase balance. Three different nitrogen-alloyed duplex grades and one superaustenitic grade were investigated. The corrosion resistance in terms of CPT, Critical Pitting Temperatue, of the super duplex material was found to be strongly correlated to the nitrogen content of the weld metal. In the case of the superaustenitic weld metal, the increased nitrogen content was found to be associated with an increased pore formation, leading to a lower corrosion resistance and thereby masking the positive effect of the increased introgen content. In order to illuminate the nitrogen exchange reactions between the arc, weld pool, and shielding gas, stationary weld experiments were also performed. The results from these stationary trials indicated that the net weld pool nitrogen content could be qualitatively understood if the various fluxes involved in the nitrogen transport between the plasma arc, weld pool and weld pool-shielding gas were considered. At short times the weld pool was limited in area and the nitrogen content of the weld pool increased due to high nitrogen activity in the arc. At longer times the nitrogen escaped from the weld pool to the shielding gas. This flux became then the dominating factor due to the increased weld pool area exposed to the shielding gas. The situation then approached the equilibrium conditions that were expected from the gas nitrogen activity and weld pool alloy composition according to thermodynamic calculations using the Thermo-Calc database.

Effect of nitrogen on impact toughness of duplex stainless steel weld metal

Summary A type 329J1 duplex stainless steel was welded by single‐pass gas tungsten arc welding in an argon‐nitrogen mixed gas atmosphere. The microstructure, Vickers hardness, and Charpy impact toughness of the weld metal were examined. The nitrogen content increases and the ferrite content decreases with increasing nitrogen partial pressure of the atmosphere. The ferrite content linearly decreases with an increasing nitrogen content. The hardness of the ferrite and austenite phases is virtually constant regardless of the weld metal nitrogen content. The toughness increases with the nitrogen content at room temperature and above, remaining constant at lower temperatures. The weld metal toughness is affected by the presence of austenite and chromium nitride precipitates in the ferrite. The nitrogen absorption of duplex stainless steel weld metal improves the impact toughness through an increase in the austenite content and a decrease in the amount of nitride.

二相ステンレス鋼溶接金属の靭性に及ぼす窒素の影響

A type 329J1 duplex stainless steel was welded by gas tungsten arc welding process in argon-nitrogen gas mixture atmosphere. The microstructure, Vickers hardness and Charpy impact toughness of the weld metals were examined. The nitrogen content increased and the ferrite content decreased with an increase in the nitrogen partial pressure of atmosphere. The ferrite content decreased linearly with an increase in nitrogen content. The hardness in each of ferrite and austenite phase was nearly constant regardless of the nitrogen content of weld metal. The toughness increased with the nitrogen content at room temperature and more, while it was constant at low temperatures. The toughness of weld metal was affected by the presence of austenite and chromium nitride precipitates in ferrite. The nitrogen absorption of duplex stainless steel weld metal improved the impact toughness because of the increase in austenite content and the decrease in the amount of nitride.

The Relationship between Quantitatively Evaluated Microstructure and Fracture Toughness on Austenitic Stainless Steel Weld Metal.

The microstructures of stainless steel weld metals which had absorbed nitrogen were analyzed quantitatively by means of a computer-aided image analyzer. Then, the relationships between quantitative microstructural factors and the low-temperature fracture behaviors were investigated. Generally, the δ ferrite which is included in the stainless steel weld metal causes cleavage fracture at low temperatures and brings about a decrease in the fracture toughness property. There is much potential for improving the toughness by controlling the amount and shape of δ ferrite. The amount of δ ferrite decreased and its shape became more globular with increasing nitrogen content in weld metal. Consequently, cleavage fractures rarely occurred at low temperature, and the fracture toughness values were improved. The δ ferrite amount (A) and the shape factor ( S ) were combined into the factor of A·S. The A·S factor has a linear relationship with fracture toughness values.